Modulation

An AutoPan simply pans automatically from left to right and back. Simple plugins just have a sinus wave, more advanced allow for more complex waveforms incl. custom waveforms.

A Flanger is similar to a Phaser but stronger. It uses a delay to create an infinite series of notches and peaks. Sounds sort of like a "whoosh".

A Phaser uses a series of all-pass filters with phase shifts that when mixed with the original sound creates a number of notches and peaks due to phase cancelling. A LFO modulate the phase shift which sweeps the notches and peaks up and down the frequency range thereby creating a spacey swirling sound.

Blue Cat's Phaser is a free phaser that reproduce the vintage phasing effect with up to 32 phasing stages. The plugin comes in both mono and stereo version; the stereo version has an additional "spread" control for a deep stereo widening phasing effects.

Price: Free

MAutopan is included in the free effects bundle from MeldaProduction. It is a very powerful auto panner. Oscillator shape can be customized. It can be free running or synced to host. Has lots of presets and smart randomization.

Price: Free

PanCake 2 from Cableguys is a easy to use auto panning tool. Use standard sinus or triangle waves or draw your own. LFO can be synced to host or free running.